Sensor mesh and signal transmission architectures for electromagnetic signature analysis

ABSTRACT

Systems and methods can support a sensor mesh and signal transmission architecture for electromagnetic signature analysis and threat detection. Sensor antennas may be deployed within an electromagnetic environment. A configurable antenna feed network can couple radio frequency signals from the antennas to both software-defined radio receivers and hardware-defined radio receivers. A raw signal analysis engine associated with the software-defined radio receiver can receive digital samples of the radio frequency signals, identify signal features within the digital samples, and generate signal feature vectors from the identified signal features. A signal feature network can receive the signal feature. A signal aggregation and analysis engine can receive the signal feature vectors from the signal feature network, aggregate the signal feature vectors, process the signal feature vectors, and identify wireless attacks according to the signal features within the signal feature vectors. One or more updatable analysis databases can support the signal processing operations.

RELATED APPLICATION

This application claims priority to U.S. Provisional Patent ApplicationNo. 62/072,884, filed Oct. 30, 2014 and entitled “Systems and Methodsfor Identifying Wireless Security Threats Via Electromagnetic Signaturesof the Internet of Things.” The complete disclosure of theabove-identified priority application is hereby fully incorporatedherein by reference.

BACKGROUND

There are billions of electronically communicating devices in use. Manyof these devices are wireless devices such as smartphones, tablets,personal computers (PCs), media players and readers, personal digitalassistants (PDAs), headsets, cameras, vehicles, wearable fitness device,health monitoring devices, and so forth. Many of these devices use someform of electromagnetic (EM) or radio frequency (RF) technology forcommunications with other devices, various communications services, andthe Internet. Many of these devices wirelessly connect to the Internetforming a growing “Internet of Things” (IoT). The number ofelectronically communicating devices is expected continue to multiplydue to business and consumer demands.

Despite the growing ubiquity of IoT devices, these devices and thenetworks connecting them remain vulnerable to wireless attacks. Onedriver in IoT device vulnerability is that there is no dominant IoTwireless networking standard. Instead, IoT devices employ one of manywireless access protocols. Some of these protocols are openly definedfor anyone to use, others are proprietary to specific manufacturers.Because of this heterogeneity, IoT networks have been constructed with aprimary objective of efficiently implementing stable wirelessconnectivity and generally assume that the wireless operatingenvironment will be absent of threats from malicious agents. As speedand stability have been primary concerns, there has been littleattention focused on the security of IoT wireless networks and theircomponents. This reliance on implicit trust leaves wireless networks andthe connected nodes vulnerable to external attacks.

IoT wireless protocols define how nodes operate on the network and mayprovide a gateway for entry to existing wired networks. Malicious agentsmay exploit these protocols to gain network access and possibly engagein undesirable network activities. Ill-defined protocols ormisconfigured configured network nodes can cause harm eitherunintentionally due to poor user operation or intentionally by allowingaccess to malicious agents.

An example malicious objective may be to degrade the target networkperformance, or ultimately deny service to legitimate users. Anotherexample may be to extract situational awareness about the targetnetwork. Yet another example may be to extract sensitive informationfrom the target network. Other goals of malicious actors may includeimpacting network routing to prevent certain packets from reaching theirintended destination or acting as an authenticated node by evadingnetwork trust mechanisms.

Emerging adaptable link layer protocols, such cognitive radio, mayimpact both attack and defense paradigms. Highly agile medium access,which may adapt due to context or environment, may result in wirelessnetwork nodes that are even more susceptible to attacks that exploitunforeseen vulnerabilities. Under this emerging paradigm, spatialdynamics may play a large role in how the network forms and operates.

There is a need in the art for architectures to detect, locate, andclassifying wireless attacks against IoT networks and devices. Sucharchitectures can support the implementation of security measuresrelated to collecting and processing electromagnetic, radio frequencyemission signatures from electronic devices for identifying potentialwireless network security threats.

SUMMARY

In certain example embodiments described herein, methods and systems cansupport a sensor mesh and signal transmission architecture forelectromagnetic signature analysis and threat detection. A plurality ofsensor antennas may be deployed within an electromagnetic environment. Aconfigurable antenna feed network can couple radio frequency signalsfrom the sensor antennas to both software-defined radio receivers andhardware-defined radio receivers. A raw signal analysis engineassociated with the software-defined radio receiver can receive digitalsamples of the radio frequency signals, identify signal features withinthe digital samples, and generate signal feature vectors from theidentified signal features. A signal feature network can receive thesignal feature vectors generated by the raw signal analysis engine. Asignal aggregation and analysis engine can receive the signal featurevectors from the signal feature network, aggregate the signal featurevectors, process the signal feature vectors to refine the signalfeatures within the signal feature vectors, and identify wirelessattacks according to the signal features within the signal featurevectors. One or more updatable analysis databases can support operationsof the raw signal analysis engine and the signal aggregation andanalysis engine.

These and other aspects, objects, features, and advantages of theexample embodiments will become apparent to those having ordinary skillin the art upon consideration of the following detailed description ofillustrated example embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram depicting an electromagnetic environment andsignature analysis system in accordance with one or more embodimentspresented herein.

FIG. 2 is a block diagram depicting a sensor incorporating asoftware-defined radio receiver in accordance with one or moreembodiments presented herein.

FIG. 3 is a block diagram depicting a processing architecture forelectromagnetic signature analysis in accordance with one or moreembodiments presented herein.

FIG. 4 is a block diagram depicting a raw signal analysis engine inaccordance with one or more embodiments presented herein.

FIG. 5 is a block flow diagram depicting a method for electromagneticsignature analysis and threat detection in accordance with one or moreembodiments presented herein.

FIG. 6 is a block flow diagram depicting a method for raw signalanalysis in accordance with one or more embodiments presented herein.

FIG. 7 is a block flow diagram depicting a method for feature vectoraggregation and analysis in accordance with one or more embodimentspresented herein.

FIG. 8 is a block diagram depicting a computing machine and a module inaccordance with one or more embodiments presented herein.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS Overview

The methods and systems described herein enable architectures fordetecting, locating, and classifying wireless attacks against IoTnetworks and devices. A network of sensors can collect radio frequencysignals. A network of signal processing engines can process thosecollected signals to identify, geolocate, group, determine intent of,and classify wireless devices in the area. Databases can manage andleverage libraries of signal and attack information. Securityadministrators may use a visualization console to monitor for wirelesssecurity threats. Technology presented herein can implement securitymeasures related to the use of detected electromagnetic, radio frequencyemission signatures from electronic devices to detect potential securitythreats.

The functionality of the various example embodiments will be explainedin more detail in the following description, read in conjunction withthe figures illustrating the program flow. Turning now to the drawings,in which like numerals indicate like (but not necessarily identical)elements throughout the figures, example embodiments are described indetail.

Example System Architectures

FIG. 1 is a block diagram depicting an electromagnetic environment andsignature analysis system in accordance with one or more embodimentspresented herein. Wireless devices 110A-110F may each engage in one ormore modes of radio communication thereby generating electromagneticsignals. The technology presented herein can collect and analyze thesesignals. Sensors 120A-120E can collect and report radio frequencysignals within the surrounding electromagnetic environment. A signalanalysis system 130 can process the collected radio frequency signals. Aconsole 140 can provide a user interface for configuring, controlling,or reviewing analysis results associated with the signal analysis system130. One or more networks 150 may interconnect some or all of thesensors 120, the signal analysis system 130, and the console 140.

The wireless devices 110A-110F may be referred to, in general orcollectively, as wireless devices 110 or a wireless device 110. Thewireless devices 110 may include smartphones, computers, wearabledevices, embedded computing devices, building system devices, industrialcontrol/automation systems, physical security systems, securitymonitoring devices, automotive systems, avionics, point of salessystems, customer tracking systems, inventory systems, wirelessdata/voice/video infrastructure, access control systems, and so forth.The wireless devices 110 may use Wi-Fi, Bluetooth, Zigbee, mobiletelephone, GSM, CDMA, satellite, LTE technology, or various otherwireless communication technologies.

The sensors 120A-120E may be referred to, in general or collectively, assensors 120 or a sensor 120. The sensors 120 may collect electromagneticsignals from one or more antennas over a wide bandwidth of radiofrequencies. The sensors 120 may utilize hardware radio receivers orsoftware-defined radio frequency receivers. According to variousembodiments, these radio receivers can convert received radio frequencyenergy into digital signals. These digital signals can then be decodedinto encoded data streams.

While hardware-defined radio receivers can be cost-effective and lesscomplex to implement, they may be limited as to what type of encodeddata streams they can detect from the electromagnetic environment. Forexample, a hardware Wi-Fi receiver module or chipset is generally notable to also receive mobile telephone radio signals. In contrast,software-defined radio receivers can much more flexibly receive anddecode various data streams within the electromagnetic environment undersoftware control. The signal data collected by the sensors 120 may betransmitted to the signal analysis system 130 for processing. Thesesignals or related signal data may be communicated in a continuousfashion or in one or more batches, at particular intervals according tovarious embodiments.

The signal analysis system 130 can receive and process signals from thesensors 120. The signal analysis system 130 may perform, among otherfunctions, raw signal analysis, signal aggregation, multiple-inputantenna processing, space-time-frequency analysis, geolocation, linkpair association, throughput estimation, classification, attackanalysis, and various other types of signal processing and analysis. Thesignal analysis system 130 may comprise a signal aggregation andanalysis engine comprised of one or more feature vector processors. Thesignal analysis system 130 may be comprised of multiple systems thatperform different portions of analysis and pass signals between eachother in various formats over various communication links of thenetworks 150. For example, the signal analysis system 130 may comprise acomplex and flexible network of various processing devices, which may bedistributed to certain degrees or layered in a hierarchical system, toanalyze and process the signals from the sensors 120.

The console 140 and various associated operator interfaces can supportconfiguring, controlling, or reviewing analysis results associated withthe signal analysis system 130. The console 140 can providevisualization features for use by security administrators to monitor theelectromagnetic environment for wireless security threats. Suchvisualizations may include displays about the area under surveillanceincluding device type, device position, pair-wise wireless communicationlinks between devices, estimates of the data throughput beingtransmitted by devices, attack types being perpetrated, victim devices,and so forth. The operator interfaces may comprise interfaces associatedwith one or more visualization consoles 140, one or more administrativeuser interface application, or various other user or system interfacesassociated with the technology presented herein.

The networks 150 may interconnect some or all of the sensors 120, thesignal analysis system 130, and the console 140. Portions of thenetworks 150 connecting the sensors may be configured to transmit radiofrequency signals and/or digital information. Radio frequency signalsmay be communicated as collected, down-converted using an intermediatefrequency oscillator, or down-converted to baseband. Communication linksassociated with the networks 150 may use various physical media such astwisted pair, coaxial cable, or fiber optic cables. The signalstransferred on the physical media may be analog RF, radio over fiber,digital, packetized, switched, connection-oriented, or any combinationthereof. According to various embodiments, the communication linksassociated with the networks 150 may use wireless frequencies ortransmission paths that are selected to avoid interference from or tothe electromagnetic environment in use by the wireless devices 110.

It should be appreciated that, according to certain embodiments, thewireless devices 110 may also make use of the networks 150. According tocertain other embodiments, the wireless devices 110 may be dissuaded orprecluded from sharing the networks 150 with the signal collection andanalysis systems presented herein and instead may connect to one or moreproduction networks that are separate from the networks 150 associatedwith the sensors 120 and/or the signal analysis system 130.

The sensors 120, or the antennas associated therewith, may be physicallydistributed around an area under surveillance. The collective coverageprovided by the sensors 120 may define the effective extent of the areaunder surveillance. According to some examples, the sensors 120 may bepositioned uniformly on a grid pattern throughout the area undersurveillance. The grid may be a square grid, hexagonal grid, or otherdistributed pattern. The spatial period of the distribution pattern maybe related to a coverage distance associated with each sensor 120. Theperiodic positioning of the sensors 120 may be altered to accommodatestructures within the environment such as walls, stairwells, mechanicalsystems, and so forth. The periodic positioning of the sensors 120 maybe altered to accommodate infrastructure feeds such as power andinterface points for the network 150. For example, the interface pointsfor the network 150 might be Ethernet ports.

Designing a location plan for the sensors 120 may start by receiving afloor plan of the proposed area under surveillance. Locations foravailable power and interface points for the network 150 may beidentified. Sensor locations may be selected to form an approximatelyuniform grid, or other spatial distribution, constrained to theidentified infrastructure locations. The sensors 120 may then bedeployed at these locations. Once the sensors 120 are collectingsignals, the number of packets, or other identified signal features, maybe tracked such that sensors 120 collecting low numbers may be evaluatedas potentially coving low traffic areas. Such low traffic sensors 120may be re-position or spaced out to improve aggregate receptionefficiency. Designing a location plan for the sensors 120 in thisfashion may be referred to as surveillance area survey planning.

Other example sensor survey mechanisms may involve calculating theexpected performance of a given sensor layout using physics-based orstatistics-based models. For example, a physics-based model maycalculate link budgets from points within the area under surveillance toeach sensor 120. From these link budgets it may be possible tocharacterize how many sensors 120 would be able to see a given point inthe area under surveillance on average. According to other examples,statistics-based site surveys may involve modeling the distribution ofreceived signal strength values for each various pairings of a sensor120 to a point in space within the area under surveillance. Statisticalestimation techniques, such as the Cramer-Rao bound, may be used toestablish a sensor location plan from the modeled signal strengthvalues. For example, a bound may be determined for the base-caselocalization error over selected points within the area undersurveillance.

One example attack type that may occur within the electromagneticenvironment can involve a wireless device 110 configured as a maliciousagent. The malicious agent may be configured as a rogue wireless accesspoint to target other wireless devices 110 as victims. The roguewireless access point may provide an unapproved wireless local areanetwork, such as a Wi-Fi network. According to certain examples,legitimate users of wireless devices 110 may scan for available wirelessnetworks and find the rogue network that has been intentionally named toappear as a trustworthy wireless network within the organization. Insome instances, one or more of the wireless device 110 mayautomatically, or manually, connect to the malicious Wi-Fi network afterassuming it to be trustworthy. Once connected, the malicious agents mayattempt to obtain passwords, bank account details, employment records,or other types of sensitive information from the victim wireless device110. Also, the malicious agents may add malicious code the victimwireless device 110 allowing further malicious actions against thevictim, other victims, or the network in general.

Application of an electromagnetic signal collection and analysis systemas presented herein can provide an area of enhanced wireless securityagainst such malicious agents. With respect to the rogue wireless accesspoint example attack, the signal analysis system 130 may be configuredto parse the malicious Wi-Fi signal and determine that the maliciousdevice is broadcasting a Wi-Fi signal to create an unauthorized wirelessnetwork. The signal analysis system 130 can send a notification to anappropriate security system or appropriate personnel. The notificationmay be made via the console 140 and may include an estimated locationfor the malicious device.

It should be appreciated that wireless security threats may take manydifferent forms such as viruses, malware, spyware, and so forth. Thethreats may be transmitted through a variety of different channels, suchas different frequencies, protocols, or wireless services. The threatsmay be designed to accomplish a variety of nefarious tasks such asshutting systems down, stealing information, denial of service attacks,device spoofing, and so forth.

The technology presented herein may support detecting and classifyingwireless attacks on wireless devices 110 and networks. The technologypresented herein may also support geolocating rogue, unauthorized, ormalicious wireless devices 110. The technology presented herein may alsosupport identifying data transfer event and estimating the amount ofdata being transmitted from a wireless device 110 using time-frequencyphysical-layer measurements of the electromagnetic environment. Thetechnology presented herein may also support classifying the modes ofwireless connectivity between wireless devices 110 using time-frequency,physical-layer measurements of the electromagnetic environment.

The console 140 can provide a user interface for security personnel orsystem administrators to obtain visibility into operations of the signalanalysis system 130 and determinations about the various wirelessdevices 110 made from the electromagnetic environment. The signalanalysis system 130 may track, monitor, record, and playback theposition and activity of the various wireless devices 110 includingsuspected rogue, unauthorized, or malicious devices. A systemadministrator, or other user, may use the console 140 to discover,track, and otherwise analyze a malicious wireless device 110 operatingwithin a wireless infrastructure. The administrator may be provided witha visualization of the position of the wireless devices 110 in theenvironment. The visualization may include metadata for each of thewireless devices 110. For each given wireless device 110, the metadatamay include physical layer specifications such as modulation, protocols,symbol rates, bandwidths, or frequencies; a likelihood metric that thedevice is rogue, unauthorized, or malicious; a type of attack, if any,being employed by the device; and other wireless devices 110 that theparticular device is likely to be communicating with.

The technology presented herein may support detecting, locating, andclassifying infected wireless devices 110. Infected wireless devices 110may have become susceptible to malicious software causing the device toperform one or more undesired behaviors. Such behaviors may includedisrupting other wireless devices 110, infecting other wireless devices110, surreptitiously recording and transmitting audio/video,transmitting sensitive data to a third party, other attacks presentedherein, or any combinations thereof. The signal analysis system 130 mayaddress such threats by detecting, geolocating, and classifying signalscharacteristic of infected wireless devices 110. The signal analysissystem 130 may alert a user, such as an administrator, to the locationof the infected wireless device 110. The alert may be provided via, orin association with, the console 140.

The technology presented herein may support detecting, locating, andclassifying wireless devices 110 that are susceptible to wirelessattack. In addition to inherent weaknesses in certain devices,protocols, or software versions, an attacker may attempt to place atarget wireless device 110 into an insecure or vulnerable state as aprecursor to the actual attack. While many wireless devices 110implement countermeasures to prevent them from being infected withmalicious software or otherwise compromised, attacks may attempt tooverride or otherwise circumvent these protections. As examples,encryption and secure authentication intended to prevent wirelessattacks, may be circumvented. A condition where a wireless device 110has been placed into such a vulnerable state may be observed from theradio emissions of the wireless device 110. The signal analysis system130 may detect, geolocate, and classify signals characteristic ofvulnerable devices.

One example of detecting a wireless device 110 that may be susceptibleto wireless attack, is identifying that a mobile telephone that isoperating in 2G mode even when 3G or 4G modes are available on thedevice and from the service provider. A threat may be in play to snooptext (SMS) messages since the 2G standard may send such messages withoutencryption. Where sensitive information, such as a password reset code,is transmitted using text (SMS) messages and an attacker has forced themobile telephone into 2G mode, the sensitive information may becompromised.

Another example of detecting a wireless device 110 that may besusceptible to wireless attack, is identifying that a Bluetooth deviceis configured to allow for unauthenticated pairings of other Bluetoothdevices. An attacker can take advantage of such a open pairing state toconnect to a Bluetooth device and extract data or install malicioussoftware.

The technology presented herein may support detecting, locating, andclassifying wireless signal jamming attacks. Wireless systems aregenerally susceptible to jamming attacks where a malicious actortransmits wireless signals with the intent of blocking the wirelessfunction of other wireless devices 110 in the vicinity. Radio jammingmay be implemented as a barrage of radio frequency noise. Moresophisticated jamming may involve a jamming signal that is crafted toefficiently and specifically target only a subset of wireless systems inthe environment that are operating on certain frequencies, using certainmodulation techniques, or implementing certain protocols. The signalanalysis system 130 may detect, geolocate, and classify jamming signals.

The technology presented herein may support detecting, locating, andclassifying impersonation attacks. Various wireless systems may besusceptible to impersonation attacks where a malicious actor transmitswireless signals with the intent of impersonating a recognized wirelesssignal. The objective of such an attack may be to control, block, orcollect information from a wirelessly connected system. Such an attackmay also target wireless mesh networks, where, through a variety ofimpersonation techniques, the attacker may change the network behaviorto achieve malicious objectives. The following four examples demonstratehow impersonation attacks may threaten various types of systems. Itshould be appreciated that these are only examples and various othertypes of impersonation attacks may be detected, located, classified, andthwarted according to the technology presented herein.

A first example of an impersonation attack is against a building controland automation system that uses wirelessly connected temperature sensorsto control the heating and cooling of a building. A wirelessimpersonation attack can impersonate the temperature sensors towirelessly signal a low temperature thereby causing the heating systemto heat the building. If, for example, the heating system is associatedwith a critical data center, excessive heat could destroy computerhardware or other systems in the data center.

A second example of an impersonation attack involves mobile or cellularwireless systems. In a mobile or cellular wireless system, base stationequipment is generally installed and operated by a mobile carrier tosupport connections from user equipment wireless devices 110. Thesewireless devices 110 include user equipment mobile devices such astelephone handsets, smartphones, paging devices, data hotspots, and soforth. A malicious agent may provide an impersonated base station thatadvertises to user equipment wireless devices 110 that it is a basestation from the mobile carrier supporting voice and data service. Auser equipment wireless device 110 may unsuspectingly connect to theimpersonated base station and route data and voice traffic through theimpersonated base station. The impersonated base station may thenmaliciously read and modify data and voice content associated with theuser equipment wireless device 110. User equipment wireless devices 110often trust the base station they are connected to as having theauthority of the mobile carrier provider and thus allow remote updatingand installation of software or firmware through the base station.Accordingly, malicious actors may leverage impersonating base stationsto install and execute unauthorized software on user equipment wirelessdevice 110.

A third example of an impersonation attack involves wireless devices110, such as onboard wireless sensors, associated with automotivesystems. These sensors may be associated with temperature, braking, tirepressure, fluid levels, safety systems, or any other components of avehicle. As an example, a tire pressure sensor may act as a wirelessdevice 110 that transmits tire pressure to a vehicle control computer.In such a system, tire pressure measurements outside of a specifiedacceptable operating range, may cause the vehicle control computer toalert the driver, limit the speed of the vehicle, signal for roadsideassistance, or carry out other specified reactions. A wireless attackerimpersonating such a tire pressure sensor may cause such reactions tooccur inappropriately, or block them from occurring as they wereintended.

A fourth example of an impersonation attack involves a building securitysystem. Building security systems often include building sensors actingas wireless devices 110. These building sensors may include doorsensors, glass-break sensors, motion sensors, thermal sensors, and soforth. Measurements or signals from the building sensors may be used bythe building security system to determine whether or not to signal analarm event. A wireless attacker can impersonate signals from buildingsensors to disguise an unauthorized entry into the building, to cause afalse alarm, or otherwise interfere with building security systemsfunctionality.

The technology presented herein may support detecting, locating,classifying, and thwarting attacks associated with spoofing controlinformation within a wireless network. By spoofing routing information,a malicious wireless device 110 can disrupt the wireless network bycreating inefficient network routes, attracting network traffic, forcenetwork traffic away from intended destinations, or otherwise disruptingor preventing normal network operations. Similarly, a malicious wirelessdevice 110 might spoof medium access control information, or otheraddressing information, to configure network nodes into a vulnerablestate.

The technology presented herein may support detecting, locating,classifying, and thwarting attacks associated with sinkhole or blackhole attacks on a wireless network. According to certain examples ofsuch an attack type, a malicious wireless device 110 may attempt to lurenetwork routes to pass through it, by advertising advantageous linkquality. This may result in creating a critical point where many, orall, routes pass and thus become exposed to network disruption, datasiphoning, or various other exploits.

The technology presented herein may support detecting, locating,classifying, and thwarting attacks associated with selective dropping orselective forwarding attacks within a wireless network. According tocertain examples of such an attack type, a malicious wireless device 110may attempt to drop certain critical network packets in order to degradenetwork performance or to force a new network topology.

The technology presented herein may support detecting, locating,classifying, and thwarting attacks associated with Sybil attacks withina wireless network. According to certain examples of such an attacktype, malicious wireless devices 110 may advertise themselves indifferent ways to different unsuspecting wireless device 110 nodes inthe network. By doing so, a malicious wireless device 110 can appear tobe multiple nodes, thereby subverting security mechanisms that depend onnetwork redundancy and distribution routing. Since fault tolerantschemes may depend upon broad network consensus to detect maliciousnodes, a Sybil attack advertising a malicious wireless device 110 asmultiple nodes can cast multiple votes and overrun the consensus ballotbox making the network appear secure to other unsuspecting wirelessdevice 110 nodes.

The technology presented herein may support detecting, locating,classifying, and thwarting attacks associated with Hello flood attackswithin a wireless network. According to certain examples of such anattack type, malicious wireless devices 110 may exploit networksemploying routing algorithms where a Hello packet advertises nodes.Malicious wireless devices 110 may break medium access rules andtransmit with high power to advertise itself to even distant networknodes. Hello flood attacks may also be used to establish a sinkhole,carry out a Sybil attack, or perform other network security exploits.

The technology presented herein may support detecting, locating,classifying, and thwarting attacks associated with wormhole attacks on awireless network. According to certain examples of such an attack type,when two malicious wireless devices 110 have access to a low-latencylink outside of the wireless network, the pair can create the perceptionwithin the network that they are artificially close to other wirelessdevice 110 nodes in the network, as though they provide a wormholethrough the network. Wormhole attacks can be used to force a network toconverge on an inefficient routing topology. Wormhole attacks can alsobe used to win routing races and more effectively spoof other networknodes.

The technology presented herein may support detecting, locating,classifying, and thwarting attacks associated with badmouthing orblacklisting attacks within a wireless network. According to certainexamples of such an attack type, malicious wireless devices 110 mayexploit consensus trust mechanisms intended to detect errant behavior. Amalicious wireless device 110 can degrade the network by reportinglegitimate network nodes as suspicious. When coupled with a Sybilattack, a malicious wireless device 110 can amplify the effect of theblacklisting by replicating mistrust reports from multiple impersonatednodes.

The technology presented herein may support detecting, locating, andclassifying wireless transmissions from wireless device 110 in anunauthorized area. Certain areas, at certain times, may be unauthorizedfor certain types of wireless transmissions. For example, medicalfacilities with sensitive medical equipment may be unauthorized for anywireless transmission that may potentially interfere with the medicalequipment. As another example, aircraft during takeoff and landing maybe unauthorized for Wi-Fi or mobile carrier communications. Varioussimilar authorization restrictions may exist in call centers, officesdealing with sensitive personal information, military installations, orotherwise secure government facilities.

The technology presented herein may support detecting, locating, andclassifying auxiliary wireless devices 110 associated with cybersecurity attacks or physical security attacks. In such attacks, wirelesssignals may be used in conjunction with other malicious methods toperpetrate physical and cyber attacks. Broadly speaking, wirelesssystems may be used to allow the attacker remote access. Wirelesssystems may be also be used to control an attack infrastructure. Oneexample of such a threat may involve card skimming at point of salessystems or automated teller machines. An attacker may position coverthardware to a card reader slot such that the covert hardware is notnoticeable by users who freely slide their cards into the point of salesystems or automated teller machine. The covert hardware may storeinformation associated with scanned cards to be wirelessly collected toa remote location.

The wireless devices 110, sensors 120, signal analysis system 130,console 140, or any other systems associated with the technologypresented herein may be any type of computing machine such as, but notlimited to, those discussed in more detail with respect to FIG. 8.Furthermore, any modules associated with any of these computing machinesor any other modules (scripts, web content, software, firmware, orhardware) associated with the technology presented herein may by any ofthe modules discussed in more detail with respect to FIG. 8. The devicesand computing machines discussed herein may communicate with one anotheras well as other computer machines or communication systems over one ormore networks such as network 150. The network 150 may include any typeof data or communications links or network technology including any ofthe network technology discussed with respect to FIG. 8.

FIG. 2 is a block diagram depicting a sensor 120 incorporating asoftware-defined radio receiver in accordance with one or moreembodiments presented herein. An antenna 210 may receive a radiofrequency signal 215. The radio frequency signal 215 may be coupled intoa radio frequency front end 220. The radio frequency front end 220 maycondition the radio frequency signal 215 to generate an analog outputsignal. The analog output signal may comprise in-phase and quadraturecomponents referred to as I and Q signals. The analog output from theradio frequency front end 220 may be coupled to a digitizer 230. Thedigitizer can output data that is a digital representation of the analogoutput generated by the radio frequency front end 220. The digitalrepresentation may be sampled in time and quantized in amplitude. Thedigital representation may also comprise separate I data and Q data. Araw signal analysis engine 240 may receive and process the raw digitalrepresentation generated by the digitizer 230. A raw signal analysisoutput 250 may be the results of processing associated with the rawsignal analysis engine 240. The raw signal analysis output 250 may becommunicated onto the network 150 for further processing.

The antenna 210 may be used to collect a broad range of radio frequencysignals from the electromagnetic environment for analysis. The antennas210 may use various antenna geometries. According to certain examples,the antennas 210 may be monopoles, dipoles, patch antennas, yagis,parabolic, horns, loops, reflector antennas, beam antennas, or any othertype of structure configured to become electrically excited by radiofrequency electromagnetic radiation of a desired frequency,polarization, or propagation direction. The antennas 210 can be locatedin various locations around a room, around a building, or withindifferent areas or floors of a building.

According to certain example embodiments of the radio frequency frontend 220, a radio-frequency band-pass filter 222 can select a channel, ora frequency range, from the radio frequency signal 215. A low noiseamplifier 224 may be used to increase the amplitude of the signal fromthe selected channel. A signal from a variable-frequency oscillator 226may be combined, or mixed, with the radio frequency signal by a mixer228. Mixing the radio frequency signal with both the signal from avariable-frequency oscillator 226 and an out-of-phase copy of theoscillator output may be used to generate both in-phase and quadrature(I and Q) components. The frequency of the variable-frequency oscillator226 may be tuned to down-convert the radio frequency signal to a lowerfrequency such as baseband, an intermediate frequency, or some otherlocal oscillator frequency.

According to certain example embodiments of the digitizer 230, alow-pass filter 232 may be applied to the I and the Q signals from theradio frequency front end 220. The low-pass filter 232 may be useful asan anti-aliasing filter before digitizing the signal. An analog todigital converter (ADC) 234 can convert the continuous, analog signalinto a digital value that represents a time sampling of an amplitudeassociated with the continuous signal. The sampling may be quantized inamplitude and may be periodic in time. The mathematical inverse of thissampling period may be referred to as the sampling frequency. The outputof the ADC 234 may be a sampled sequence of digital values that havebeen converted from a continuous-amplitude and continuous-time analogsignal to a discrete-amplitude and discrete-time digital signal.According to certain embodiments, both I and Q signal components may beseparately filtered and converted. Accordingly, there may be twoseparate low-pass filters 232 and two separate analog to digitalconverters 234.

The raw signal analysis engine 240 may be implemented in software,firmware, programmable logic, or other such flexible technology.Accordingly, the raw signal analysis engine 240 may be considered as(all, or part of) the software portion of the software-defined radioreceiver. The raw signal analysis engine 240 can process a digitalrepresentation of the raw collected radio frequency signal 215. The rawsignal analysis engine 240 may receive digital I and Q signal samplesfrom the digitizer 230. The received samples may be processed andrefined to a discrete set of feature vectors. A signal feature vectormay be a set of values representing attributes of the signal. Featurevectors may be passed from one stage of analysis or processing toanother. At each step, attributes may be added or subtracted from thefeature vector further refining the attributes of the particular signal.Such refinement of the feature vector may support identifying,classifying, or otherwise interpreting the content of the signal. Duringthis hierarchical and/or iterative interpretation of the signal variousmodifiers or descriptors indicating features or attributes of the signalmay be appended to the feature vectors at each processing step. Someexamples of these modifiers or descriptors may include geolocationparameters, signal duration, signal bandwidth, signal angle, modulationtype, and so forth. It should be understood that the feature vectors maybe processed and re-processed by the raw signal analysis engine 240 anynumber of times in order to refine description of signal contents fromthe collected radio frequency signal 215.

The raw signal analysis engine 240 may generate a raw signal analysisoutput 250. The raw signal analysis output 250 may be a condensedcollection of intelligible features and data as identified within thecollected radio frequency signal 215. According to one or moreembodiments, the signal data may be processed and refined into featurevectors that define various attributes of the signal. The raw signalanalysis output 250, including such feature vectors, may be transmittedonto the network 150 for further processing and analysis. Thisprocessing and analysis may be carried out in association with thesignal analysis system 130.

It should be appreciated that aspects of the receiver presented hereinmay be programmable, adjustable, or otherwise controllable. In additionto the software (or otherwise flexible) portion of the receiver, agilityand configurability may be supported by elements of the radio frequencyfront end 220 and the digitizer 230 that are programmable, adjustable,or otherwise controllable. Parameters associated with these elements mayinclude a pass-band of the band-pass filter 222, a gain of the low noiseamplifier 224, a frequency of the oscillator 226, a cut-off response ofthe low-pass filter 232, a sampling rate of the ADC 234, and so forth.

It should be appreciated that while certain example sensors 120presented herein may be software-defined radios, other example sensors120 may be hardware-defined radios or simply hardware radios. Generally,a hardware radio is fixed to operate on predefined frequencies,bandwidths, modulation techniques, coding, protocols, and wirelesscommunications standards. For example, a hardware radio may bespecifically designed to receive one specific standard such as Wi-Fisignals, Bluetooth signals, or mobile telephone signals. In contrast, asoftware-defined radio may be reconfigurable using software to handleany number of different communication standards even custom or otherwisenon-standards-driven wireless communications. It should be appreciatedthat a hardware radio is often highly integrated, specifically designedfor its single purpose, and thus considerably less costly to implementthan a software-defined radio. Accordingly, it may be said that there isa tradeoff between cost and flexibility when comparing hardware radiosand software-defined radios. Software-defined radios are generally muchmore flexible but considerably more costly while hardware radios aregenerally less flexible but also less costly.

It should be appreciated that, according to certain embodiments, thesensors 120 presented herein as part of an electromagnetic monitoringand detection network may share hardware and/or software resources withproduction networks used by wireless devices 110 associated with endusers. For example, a sensor 120 used for monitoring the electromagneticenvironment may also be used to supply certain wireless communicationsfeatures. According to certain examples, wireless communicationcomponents (such as wireless access points) that support wirelesscommunications for a production network of an origination may integratefeatures and functionality presented herein for collectingelectromagnetic signals for signature or threat analysis.

FIG. 3 is a block diagram depicting a processing architecture forelectromagnetic signature analysis in accordance with one or moreembodiments presented herein. A plurality of antennas 210 may be coupledto one or more receivers via an antenna signal-switching network 310.The receivers may comprise one or more software-defined radios 335. Thereceivers may also comprise one or more hardware-defined radios340A-340B. The hardware-defined radios 340A-340B may be referred to, ingeneral or collectively, as hardware-defined radios 340 or ahardware-defined radio 340. Each of the software-defined radios 335 maycomprise a radio frequency front end 220, a digitizer 230, and a rawsignal analysis engine 240. The raw signal analysis engines 240 may becoupled to the digitizers 230 via a raw digital signal switching network320. The outputs of the receivers, both the software-defined radios 335and the hardware-defined radios 340, may be coupled through one or morelayers, or stages, of a signal feature vector network 330. Variousmodules associated with the signal analysis system 130 may furtherprocess these receiver outputs. These modules may include, for example,space-time-frequency analysis 350, geolocation 355, pair-wise linkassociation 360, data throughput estimation 365, device classification370, and attack classification 375. Operations of the raw signalanalysis engine 240 and/or the various modules associated with thesignal analysis system 130 may be supported by various analysisdatabases 380.

The antenna signal-switching network 310 can support switching androuting radio frequency signals 215 received by the antennas 210 tovarious radio receivers. Accordingly, the antenna signal-switchingnetwork 310 may be referred to as an antenna feed network. The radioreceivers may include both the software-defined radios 335 as well asthe hardware-defined radios 340. The radio frequency signals 215 may becoupled from the antennas 210 using coaxial cable or other conductivetransmission line or waveguide technology. The radio frequency signals215 may also be coupled from the antennas 210 using radio frequency tooptical converters, optical modulators, radio-over-fiber technology, orother techniques for transmitting the signal over optical fiber or otheroptical waveguides. The radio frequency signals 215 may be switchedwithin the antenna signal-switching network 310 using mechanicalswitches, electromechanical switches, radio frequency switches,semiconductor switches, optical switches, electro-optical switches, orother signal path switching technology.

The antenna signal-switching network 310 can support switching androuting the radio frequency signals 215 from one particular antenna 210between some or all of the receivers within the system. According tocertain embodiments, the antenna signal-switching network 310 may befully interconnected, wherein any of the antennas 210 may be switched toany of the receivers. According to certain other embodiments where theantenna signal-switching network 310 may support a lesser degree ofinterconnectivity, a subset of the antennas 210 may be switchablebetween a subset of the receivers. According to some embodiments,certain receivers may be directly coupled to certain antennas 210without being switchable.

The antenna signal-switching network 310 may comprise various switchingtopologies such as matrix, crossbar, one-to-many, many-to-one, fan-out,sparse fan-out, star, ring, any other structure, or any combinationthereof. The antenna signal-switching network 310 may be controlledmanually or automatically by any of the computing machines or modulespresented herein. The antenna signal-switching network 310 may compriseone or more direct radio frequency interconnections, one or more radiofrequency signal switches, one or more radio frequency signal splitters,and various other mechanisms for switching and routing radio frequencysignals.

One reconfiguration example associated with the antenna signal-switchingnetwork 310 may involve receiving a Bluetooth wireless signal. Accordingto the example, upon determining that the particular radio frequencysignal 215 detected at a particular antenna 210 contains a Bluetoothsignal, the signal analysis system 130 may use the antennasignal-switching network 310 to redirect that particular radio frequencysignal 215 from a software-defined radio 335 instead to ahardware-defined radio 340 specifically designed to receive and decodeBluetooth signals. Such automated reconfiguration may improvespecialized decoding of the Bluetooth signal while also freeingresources within the software-defined radio 335 from tasks moreefficiently suited to the appropriate hardware-defined radio 340. Itshould be appreciated that while Bluetooth was specified in this signalpath reconfiguration example, the same benefits may apply to wirelesscommunication modalities other than Bluetooth where an appropriatehardware-defined radio 340 is available to offload tasks from asoftware-defined radio 335.

It should also be appreciated that while the Bluetooth signal-pathreconfiguration example used a Bluetooth signal received at asoftware-defined radio 335 to cue switching the radio frequency signal215 to a hardware-defined radio 340, other example scenarios may involvea signal received at a hardware-defined radio 340 being used to cueswitching the radio frequency signal 215 to a software-defined radio335. For example, the radio frequency signal 215 may be redirected to asoftware-defined radio 335 that is capable of smart-antenna processingwhile the original hardware-defined radio 340 was configured to handleonly one radio frequency input. Smart-antenna processing can combine theradio frequency signal 215 from two or more antennas 210. This may bereferred to as beam forming, MIMO, and so forth. Multiple antennasources may be combined in order to directionally discriminate thesource wireless device 110 for a desired electromagnetic emission. Suchdirectionality may be computationally obtained from multiple antennasources instead of physically orienting a directional antenna.Directionality can support extracting a weak signal, differentiating asignal from various interferers, or otherwise improving reception of asignal that presented poorly at a single antenna 210 or even multipleoriginal antennas 210. The antenna signal-switching network 310 cansupport matching the proper antennas 210 to the proper receiver inputsfor optimizing smart-antenna processing. While one or more of thehardware-defined receivers 340 may be configured to supportsmart-antenna processing through multiple antenna inputs, thesoftware-defined receivers 335 may inherently support smart-antennaprocessing through computationally combining the sampled signals frommultiple digitizers 230 during the software portion of the receiveroperation.

The antenna signal-switching network 310 may also incorporate one ormore splitters. The splitters may be used to replicate the particularradio frequency signal 215 a number of times for distribution to two ormore receivers. For example, a hardware receiver 340 may be assigned toextract a Wi-Fi signal from the radio frequency signal 215 at the sametime that a copy of the radio frequency signal 215 may be routed to asoftware-defined receiver 335 to process some other signals detected atthe same antenna 210. According to certain embodiments, smart-antennaprocessing can cue combining of signals within the antennasignal-switching network 310. It should be appreciated that the numberof antennas 210 and the number of receivers may not be the same. Forexample, there may be additional antennas 210 to allow a choice of whichantennas 210 may be routed to the receivers through the antennasignal-switching network 310. According to other embodiments, there maybe fewer antennas 210 than receivers, or the numbers may be similar oreven the same.

The antenna signal-switching network 310 can support intelligentallocation of the radio frequency signal 215 from the various antennas210 to the various receivers. For example, complicated signal analysiscases, or those requiring directional processing, may be routed to oneor more software-defined receivers 335 while signals may be routed toefficient and inexpensive hardware-defined radios 340 where appropriate.The more flexible the antenna signal-switching network 310, the moreoptimally the signal processing allocation may be made between thevarious resources within the system.

The software-defined radios 335 generally comprising radio frequencyfront ends 220, digitizers 230, and one or more digital signalprocessing stages to computationally process outputs from the digitizers230. The digital signal processing stages may include the raw signalanalysis engines 240. The digital signal processing stages may alsoinclude one or more modules associated with the signal analysis system130. These modules may include, among other example modules,space-time-frequency analysis 350, geolocation 355, pair-wise linkassociation 360, data throughput estimation 365, device classification370, and attack classification 375. It should be appreciated that inaddition to the illustrated embodiment that separates the raw signalanalysis engines 240 from the signal analysis system 130, various otherembodiments may incorporate the raw signal analysis engines 240 with oneor more of the modules associated with the signal analysis system 130.Such incorporated digital signal processing stages may be consideredeither (or both) part of the raw signal analysis engines 240 or part ofthe signal analysis system 130 without departing from the scope orspirit of the technology presented herein.

The raw signal analysis engine 240 may receive digitally sampled I and Qsignals from the digitizer 230. The raw signal analysis engine 240 canprocess this digital representation of the raw collected radio frequencysignal 215 to generate a discrete set of feature vectors. For example,the raw signal analysis engine 240 may perform time-frequency analysisof the radio frequency signal 215 from a particular antenna 210. Thetime-frequency information from the radio frequency signal 215 may beencoded as a feature vector. For example, time-frequency bins may bedefined and the spectral intensity of the radio frequency signal 215corresponding to each time-frequency bin may be represented within thefeature vector. The raw signal analysis engine 240 may also performangle analysis where an angle dimension for the radio frequency signal215 may be added to each feature vector. The raw signal analysis engine240 may also perform modulation classification and signal decoding wherefeature vectors may be refined by appending dimensions representingadditional features associated with modulation and decoded signalcontents.

The raw digital signal switching network 320 can switch and route theoutputs from one or more digitizers 230 to the inputs of one or more rawsignal analysis engine 240. The output from each digitizer 230 may be astream of digital I signal samples and digital Q signal samples. The Iand Q samples may be communicated as two separate streams or as a singlecombined or interleaved stream. These streams may be routed to theappropriate raw signal analysis engines 240 at packetized data or as aclocked (or asynchronous) stream of parallel or serialized data.Switching and routing within the raw digital signal switching network320 can allocate the output each digitizer 230 to the most appropriateand available raw signal analysis engine 240 according to one or moremetrics such as route distance, resource capacity, performance,availability, cost, and so forth.

The signal feature vector network 330 can switch and route signalfeature vectors between the raw signal analysis engines 240 and thevarious other modules associated with the signal analysis system 130.The signal analysis system 130 may comprise a signal aggregation andanalysis engine comprised of one or more feature vector processors. Thesignal feature vectors may be transported within the signal featurevector network 330 as packetized data or streaming data. Generally, asignal feature vector may be a set of values representing attributes ofa particular signal. In various embodiments, as a feature vector ispassed from one processing module or stage to the next, attributes maybe added or subtracted from the feature vector, further refining theattributes of the particular signal to better identify and/or classifythe contents of the signal. Feature vectors may be appended for variousfeature attributes relevant to the processing at each module orprocessing stage. According to one particular example, a geolocationfeature vector may indicate a feature vector that has geolocationfeatures added to its set of attributes. The geolocation feature vectormay include, the specific geolocation features of the signal, as wellvalues indicating duration of the signal, bandwidth of the signal, angleof the signal, a modulation type of the signal, and so forth.

The radio frequency signals 215 captured form the electromagneticenvironment by the sensors 120 may be used in detecting, classifying,and mitigating wireless attacks against one or more wireless devices110. Various digital signal processing stages may be applied to thesignals collected by the sensors 120. These digital signal processingstages may comprise modules of the signal analysis system 130 includingone or more raw signal analysis engines 240. Various sensor mesharchitectures comprising the sensors 120, the antenna signal-switchingnetwork 310, the raw digital signal-switching network 320, and thesignal feature vector network 330 can support collecting andappropriately transporting signals from the electromagnetic environmentfor signature and wireless threat analysis. Similarly, variousprocessing architectures comprising modules of the signal analysissystem 130 including one or more raw signal analysis engines 240 cansupport the various processing states of these signals for signature andwireless threat analysis.

The signal analysis system 130 can aggregate and process the variousradio frequency signals 215 captured form the electromagneticenvironment by the sensors 120. Example modules of the signal analysissystem 130 may include space-time-frequency analysis 350, geolocation355, pair-wise link association 360, data throughput estimation 365,device classification 370, and attack classification 375. It should beappreciated that the various modules of the signal analysis system 130may receive sampled signals and/or signal feature vectors from one ormore software-defined radios 335. Similarly, any data, packets, signallevels, channel parameters, error conditions, or other parametersobtained by one or more hardware-define radios 340 may be relayed to thevarious modules of the signal analysis system 130 for processing. Sincea hardware-define radio 340 may perform its own raw signal analysis andoutput information specific to its design, outputs from varioushardware-define radios 340 may be translated to radio-specific signalfeature vectors. These particular signal feature vectors may be limitedby the particular output space of any given hardware-define radio 340.

The space-time-frequency analysis module 350 can process refined featurevectors from multiple sensors 120 and match them up to a commonreference frame. The space-time-frequency analysis module 350 can alsoresolve redundant signal detection when the same signal is detected atmore than one sensor 120.

The space-time-frequency analysis module 350 can perform signalclustering and association. Feature vectors from multiple sensors 120may be clustered into common groups. Clustering may be supporting usinga k-nearest neighbors (KNN) algorithm, a hierarchical clusteringalgorithm, an expectation maximization algorithm, or any otherclustering algorithm. A specific clustering algorithm may be chosen tomaximize system performance. For example, a Monte Carlo approach may beused to evaluate multiple clustering algorithms against a referencesignal set to select the clustering algorithm that maximizes aparticular system performance objective. The system performanceobjective function may be an aggregation of performance metricsincluding signal detection accuracy, modulation classification accuracy,attack classification accuracy, and processing speed.

The space-time-frequency analysis module 350 can perform featureextraction. Feature extraction can cull disparate refined featurevectors from multiple sensors 120 into an aggregate feature vector thatrepresents all of the information about wireless devices 110 in theenvironment with minimal, or significantly reduced, redundancy. Certaindimensions of aggregated feature vectors may provide identical valuedacross multiple sensors 120. These may include duration, bandwidth,center frequency, and duty cycle, among others. Certain other dimensionsof aggregated feature vectors may be maintained as a list of potentiallydisparate values, with each value corresponding to a single sensor 120.For instance, the dimensions of the aggregate feature vectorsrepresenting a power and an angle of a signal may vary across sensors120.

The geolocation module 355 can receive the aggregate feature vector set.Geolocating signals in an environment that is dense with other signalsand contains complex propagation effects like multipath and Dopplershift can present several challenges. To aid in estimate the position ofeach signal, propagation modeling may leverage a database of sensorpositions and various parameters associated with the propagationenvironment. The database may be populated through various possiblecalibration techniques. According to a particular example, thecalibration may involve transmitting from wireless devices 110 withknown positions. Each sensor 120 can record the received power of eachof the reference emissions from the wireless devices 110 with knownpositions. From all of the known values, a parametric fit for theunknown propagation values may be performed. According to one example ofthis approach, the collected receiver power from the i^(th) referenceemitter received by the r^(th) sensor 120 may be represented as:

P _(i,r) =a/d _(i,r) ^(n)

where a and n are the unknown calibration parameters to be estimated andd_(i,r) is the known distance between the i^(th) reference emitterwireless device 110 and the r^(th) sensor 120. When the number ofsensors 120 is given as R and the number of reference emitter wirelessdevices 110 is given as I, then the calibration process results in R×Iequations in two unknowns. Various optimization methods may be used tosolve for the unknowns including, but not limited to, least-squaresestimation, minimum-mean-square estimation, constrained optimization,and so forth.

Propagation modeling functionality of the geolocation module 355 mayleverage the calibration parameters, signal power and angle values, anda coordinate system of locations for the sensors 120 to calculate aforward model of the expected power and angle values for sample pointsin space. According to particular embodiments, the model values may beused to create an initial geolocation estimate using multilaterationtechniques. The initial geolocation estimate may be used to seed amodel-matching filter. The model-matching filter can evaluate multipleaggregated feature vectors in series. For each aggregate feature vector,the model-matching filter may initialize an ensemble of hypothesizedsignal source positions around the initial seed position. In aniterative process using the model values, a tighter estimate of theaggregate feature vector position may be generated for the wirelessdevice 110 being located. As part of each iteration, hypothesizedpositions that do not fit the model may be removed. After a sufficientnumber of iterations, the position estimate for the aggregate featurevector may converge to a single point. This approach may be repeated forall aggregate feature vectors.

Model tracking may use a similar technique of hypothesized positions,however the hypothesis set may also include a range of time steps.Multiple iterations of hypothesized trajectories (or tracks) may beexamined where prior information about the likelihood of each trajectorymay be considered in the model. By filtering out unlikely tracks, atrack may be converged that best fits the data. For example, it islikely that a mobile device will be traveling at 2 m/s, but it isunlikely that it will be traveling at 200 m/s. Accordingly, a trackindicating an aggregate feature vector from a mobile device traveling at200 m/s may be filtered out of the model. Resultant geolocation trackdata may be incorporated into the aggregate feature vector to create afeature vector that includes location data.

The pair-wise link association module 360 may determine a link pair ofwireless devices 110. Generally a signal emanates from a source wirelessdevice 110 and is intended for one or more destination wireless devices110. The emitting device and a receiving device may constitute a linkpair. Information about link pairings may be useful in inferring thebehavior and intent of wireless devices 110 within a network.

Modulation association may be implemented within the pair-wise linkassociation module 360. Generally, wireless devices 110 within awireless network participate in pair-wise links between devices. Thepair-wise link association module 360 can infer these pair-wise linksfrom observed wireless features such as modulation, position,space-time-frequency occupancy, and so forth. Modulation association cananalyze modulation feature information to calculate a likelihood thatany pair of wireless devices 110 are communicating with one another.

Pair-wise links may also be determined by examining decoded messagecontents. For example, Wi-Fi header fields explicitly indicate adestination MAC address. When it is not clear from the decoded signalwhich pairs of wireless devices 110 is communicating, thenspace-time-frequency association may be used to perform a more nuancedevaluation for likely communication pairs. Signal pairing mechanismssuch as time division duplexing (TDD), frequency division duplexing(FDD), or space division duplexing (SDD) may indicate communicatingpairs of wireless devices 110. Space-time-frequency feature informationfor each geolocation feature vector may be used to determine whichsignals could feasibly be communicating with one or more known duplexingschemes. For example, if a first geolocation feature vector and a secondgeolocation feature vector both occupy the same frequency, but never atan overlapping time, it may be inferred that the wireless devices 110associated with those vectors may be a communicating pair using TDD.Feature vectors successfully evaluated by the pair-wise link associationmodule may be appended with a new set of feature vectors that containthe pairwise link information. These may be referred to as pairwisefeature vectors.

The data throughput estimation module 365 can estimate an amount of datain each pairwise feature vector. Even when signal content data is notdirectly decoded, its spectral occupancy may serve as a proxy for theamount of data that is being passed through each link wireless devices110 associated with each pairwise feature vector. This estimation mayoccur on two levels. The first level, spectrogram analysis, can useShannon's capacity formula

C=B log(1+SNR)

to bound the maximum amount of data transfer, where B is the occupiedbandwidth and SNR is the signal to noise ratio. These two parameters maybe estimated using the features estimated the signal analysis system130. Specifically, B can be directly calculated from spectrogramanalysis and SNR can be calculated from the average power andgeolocation data. The second level, modulation and link analysis, canleverage a signal signature database containing data throughput valuesfor various known signal modulation schemes. By pairing the modulationfeature values included in the pair-wise feature vector with the signalsignature database entries, modulation and link analysis can provide areasonably accurate estimate of the data throughput for each pair-wisefeature vector. An estimate of the data throughput for each signal maybe added to each corresponding pair-wise feature vector. The amendedpair-wise feature vector may now be referred to as a data throughputfeature vector.

The device classification module 370 can classify wireless devices 110as being either benign or malicious (also referred to as unauthorized orrogue). Devices classification can function to identify each pairwisefeature vector as either benign or malicious. The device classificationmodule 370 can perform signature matching, which attempts to match thesignal and link features of each data throughput feature vector to knownexamples of benign and malicious devices in the signal signaturedatabase. The device classification module 370 can further performanomaly analysis, which compares the features associated with each datathroughput feature vector into an aggregate metric. If the aggregatemetric exceeds one or more established anomaly thresholds the associatedwireless device 110 may be flagged as malicious or potentiallymalicious. The device classification module 370 can also performlocation analysis or geo-fencing, which evaluates the geolocationfeatures associated with each feature vector. If an unauthorizedwireless device 110 is identified to be within in a restricted area,then the wireless device 110 may be flagged as malicious or potentiallymalicious.

The attack classification module 375 can determine the type of attackbeing perpetrated by a malicious wireless device 110. The attackclassification module 375 can also determine if multiple maliciouswireless devices 110 are involved in the attack and which victimwireless devices 110 are being attacked. The attack classificationmodule 375 can support attack matching, which can use a library ofattack templates to match malicious wireless device 110 activities toknown attacks such as spoofing, DoS, jamming, wormholes, and othersdiscussed herein or known in the art. The attack classification module375 can support determination of attacking radios where the pair-wiselink features of a malicious wireless device 110 may be used to identifya network of multiple attacking wireless devices 110. Such a network ofmultiple attacking wireless devices 110 may also be identified withoutusing pair-wise link information depending upon the type of attack. Forexample, a pair of wireless devices 110 that have been classified asmalicious may be clearly jamming on one frequency, but may also becommunicating TDD on a second frequency. The attack classificationmodule 375 can support determination of attacking radios to identifythese two malicious wireless devices 110 as part of a malicious networkexecuting a distributed jamming attack. The attack classification module375 can support determination of victim radios for creating a list ofwireless devices 110 being attacked by a network of attacking wirelessdevices 110. According to the distributed jamming attack example, thevictim wireless devices 110 may be any network of benign wirelessdevices 110 using the frequency that is being jammed by the maliciouswireless devices 110 of the attack network.

The attack classification module 375 can support attack intent inferenceto determine a high-level intent for a network of wireless devices 110.Attack intent inference can use an attack database and informationregarding the locations and sizes of the networks. Regarding thedistributed jamming attack example, if the victim wireless devices 110being jammed are part of a closed-circuit video surveillance system,attack intent inference may indicate that the intent of the attack is todisable video. If, on the other hand, the victim wireless devices 110are cellular telephones located in a boardroom, attack intent inferencemay indicate that the intent of the attack is to block mobile carriercommunications in and out of the boardroom.

The analysis databases 380 may include, among various other examples,signal databases, sensor position databases, calibration databases,signal signature databases, and attack databases. One or more of thesignal processing and threat analysis stages of the signal analysissystem 130, including the raw signal analysis engines 240, may leveragethe analysis databases 380. The analysis databases 380 may containvarious forms of information useful in analyzing the radio frequencysignals collected by the sensors 120. Portions of the information withinthe analysis databases 380 may be preinstalled at the purchase,installation, or configuration of the sensors 120, the signal analysissystem 130, and/or other systems supporting the technology presentedherein. Portions of the information within the analysis databases 380may be configured in the field. Such configuration may be performedmanually, or autonomously through automated learning, tuning, oradaptation procedures. Portions of the information within the analysisdatabases 380 may be updated from time to time from a central provider,from backups, or from other installations. One or more central providersmay receive related information that was learned or adapted in fieldedinstallations. The received information may be incorporated intoperiodic updates provided by the central provider to the various fieldedinstallations of the technology presented herein.

It should be appreciated that while the analysis databases 380 aregenerically referred to as databases, the information may be storedwithin tables, relational databases, other types of databases, flatfiles, memories, lists, data blobs, data structures, or any other datastorage or organization technology. The analysis databases 380 may bestored locally at the signal processing and threat analysis modules ofthe signal analysis system 130 and the raw signal analysis engines 240,within one or more systems attached via the networks 150, online, in astorage cloud, in any other location, or any combination thereof. Itshould be appreciated that the analysis databases 380 may be distributedat the level of the sensors 120, distributed at the level of the signalprocessing and threat analysis modules of the signal analysis system130, centralized at the building level, centralized at the campus level,centralized at the enterprise level, or centralized at the level of oneor more providers. Various other granularities or localities of storagefor the analysis databases 380 may also be supported with departing formthe spirit or scope of the technology presented herein.

The analysis databases 380 may include one or more signal databases. Theraw signal analysis engines 240 may leverage the signal databases. Thesignal databases may comprise information that represents features ofknown signals to be matched or correlated against received signals. Thesignal databases may also comprise appropriate codecs and drivers fordecoding variously modulated signals.

The analysis databases 380 may include one or more sensor networkposition databases and one or more calibration databases. Thespace-time-frequency analysis module 350 and the geolocation module 355may leverage the sensor network position databases and the calibrationdatabases. The sensor network position databases may include thephysical positions of various sensors 120 within the environment. Thecalibration databases may include various parameters associated withelectromagnetic wave propagation within the wireless communicationenvironment.

The analysis databases 380 may include one or more signal signaturedatabases. The pair-wise link association module 360, the datathroughput estimation module 365, and the device classification module370 may leverage information from the signal signature databases. Thesignal signature databases may contain mappings from signal features tosignal types. The signal signature databases may function as a look-uptable for the signal analysis and aggregation operations.

The analysis databases 380 may include one or more attack databases. Theattack classification module 375 may leverage information from theattack databases. The attack databases may contain information or signalfeatures that are indicative of specific attack types. The attackdatabases may be used in conjunction with signals collected from thesensors 120 to identify types of attacks being perpetrated by maliciouswireless devices 110.

The raw signal analysis engine 240, signal analysis system 130, systemsassociated with the analysis databases 380, or any other systemsassociated with the technology presented herein may be any type ofcomputing machine such as, but not limited to, those discussed in moredetail with respect to FIG. 8. Furthermore, any modules (such as thoseassociated with space-time-frequency analysis 350, geolocation 355,pair-wise link association 360, data throughput estimation 365, deviceclassification 370, or attack classification 375) associated with any ofthese computing machines or any other modules (scripts, web content,software, firmware, or hardware) associated with the technologypresented herein may by any of the modules discussed in more detail withrespect to FIG. 8. The computing machines discussed herein maycommunicate with one another as well as other computer machines orcommunication systems over one or more networks such as the antennasignal-switching network 310, the raw digital signal-switching network320, and the signal feature vector network 330. It should be appreciatedthat the antenna signal-switching network 310, the raw digitalsignal-switching network 320, and the signal feature vector network 330may be associated with or share resources with the network 150. Thesenetworks may include any type of data or communication links or networksincluding any of the network technology discussed with respect to FIG.8.

FIG. 4 is a block diagram depicting a raw signal analysis engine 240 inaccordance with one or more embodiments presented herein. The raw signalanalysis engine 240 may receive digital I and Q signal samples forprocessing. Processing modules of the raw signal analysis engine 240 mayinclude, among other examples, time-frequency analysis 410, angleanalysis 420, modulation classification 430, and signal decoding 440.The processing modules, particularly the modulation classificationmodule 430, and the signal decoding module 440, may leverage a signaldatabase 450. Outputs from the raw signal analysis engine 240 may becommunicated onto the network 150.

Once received by the raw signal analysis engine 240, the digital I and Qsignal samples may be processed and refined to a discrete set of featurevectors. It should be understood that the feature vectors may beprocessed and re-processed by the various modules associated with theraw signal analysis engine 240 any number of times before beingtransmitted to the other modules of the signal analysis system 130.

The time-frequency analysis module 410 can generate a set offrequency-domain data vectors for each radio frequency signal 215. Thespectrum intensity for each time-frequency bin associated with thefrequency-domain data vectors may be encoded as dimensions of featurevectors for each of the radio frequency signals 215.

The time-frequency analysis module 410 can perform a moving windowprocess where N time samples are selected to be processed. The value ofN may be adjusted to optimize performance. A fast Fourier transform(FFT) may be computed for the N samples of the window. The FFT outputmay represent the spectral energy content of the window. The FFT of avector of samples x may be defined by the matrix-vector product

y=Qx, where the (i,k) element of Q is exp(−2*pi*i*Vj/N)

and j is the square root of negative one. As new samples of the inputsignal arrive, the moving window may slide by K samples to a new set ofN samples. The value of K may be optimized to maximize the systemperformance. According to one example, such optimization may beaccomplished with a Monte Carlo approach where various values of N and Kare tested on a reference signal set and the values of N and K thatmaximizes a system performance objective function may be selected forused. The system performance objective function may be an aggregation ofperformance various metrics. These metrics may include, among otherexamples, signal detection accuracy, modulation classification accuracy,malicious/benign classification accuracy, attack classificationaccuracy, or processing speed. The output of the FFT may be a sequenceof P frequency-domain data vectors y_(p). The collection of these datavectors can be plotted to show the time-frequency energy in the RFenvironment. This plot is commonly referred to as a spectrogram.

The time-frequency analysis module 410 can perform energy clustering andassociation. The frequency-domain data vectors from the FFT may beevaluated for each radio frequency signal 215 received at eachrespective antenna 210. Each radio frequency signal 215 may containmultiple signals received at the associated antenna 210. Energyclustering and association can perform a clustering analysis on each setof frequency-domain data vectors to determine discrete contiguous blocksof signal that are likely to have been transmitted from the same device.Clustering algorithms such as k-nearest neighbors (KNN), hierarchicalclustering, expectation maximization, or any others may be used toperform the clustering. Spectrum feature extraction may be performed oneach cluster. Spectrum feature extraction can analyze the clusters toextract a set of signal features including, but not limited to,duration, bandwidth, center frequency, duty cycle, and average power.

As an example of cluster analysis, each cluster can be considered a setof points in the multi-dimensional feature space. The objective of thecluster analysis can be to determine the representative characteristicsof the signal that corresponds to each cluster. Accordingly, statisticalmeasures such as the mean, median, or mode of each dimension may becalculated and then taken to represent the signal as that featuredimension. Each cluster can make up a discrete instance of a featurevector. Each feature vector includes one or more of the feature valuesthat implicitly characterize the signals in the environment. Featurevectors created by the time-frequency analysis module 410 may be theinputs to the angle analysis module 420.

It should be appreciated that spectrum feature extraction performed bythe time-frequency analysis module 410 may be a similar operation as thefeature extraction performed by the space-time-frequency analysis module350. However, the space-time-frequency analysis module 350 may beconfigured to cull the disparate refined feature vectors from multipleradio frequency signal 215 (from multiple antennas 210) where themultidimensional cluster of points in feature space may be statisticallyanalyzed to extract a representative value in each feature vector.According to various embodiments, the space-time-frequency analysismodule 350 preforms an analysis similar to the time-frequency analysismodule 410, but does so with multiple refined feature vectors.

The angle analysis module 420 can add an angle dimension to each featurevector. The result is a feature space that also includes an angledimension since the feature vector is amended to include an angleestimate. The angle analysis module 420 can sweep through a range ofantenna phases. Various phase combinations of the antennas 210 may beused in order to discriminate the source of an emission by an anglerelative to the antennas 210. For example, a complex-valued sample maybe taken from the frequency-domain data vectors of each of L antennas120. A vector z may be formed of these samples. A linear combination ofthe elements of z may be defined by multiplying by a point vector w(a)that is a function of the angle of interest, a. The resulting vectorproduct w(a) z is a scalar value that indicates the intensity of thetime-frequency energy in the angle direction a. According to particularembodiments, by sweeping through a range of a values, the angle analysismodule 420 can determine an energy over a space-time-frequency (STF)data cube. Angle interference suppression may be performed on the STFdata cube to filter out irrelevant RF signals. The angle analysis module420 can then perform angle clustering and association on the filtereddata cube. Angle clustering and association can refine the featurevector based on the angle information. The resulting updated set offeature vectors may be referred to as angle feature vectors. Each anglefeature vector can include characteristics about each signal, such asduration, bandwidth, center frequency, duty cycle, average power, andangle.

The modulation classification module 430 can compare the angle featurevectors to features of a library of known signals. The known signals maybe retrieved from the signal database 450. The modulation classificationmodule 430 can perform classifications by matching an angle featurevector to a feature vector of a known signal. The matching may seek tominimize a distance metric within a multidimensional feature space.Various alternative distance metrics may be used including, amongmultiple other examples, Euclidean distance, weighted-sum distance,min-max distance, and so forth. The choice of distance metric may be aparameter of the system this can be optimized to maximize performance.Outputs from the modulation classification module 430 may be anglefeature vectors that also include modulation types. These may bereferred to as modulation feature vectors.

The signal decoder module 440 can decode messaging layer content frommodulation feature vectors. Generally, decoding payload data from thewireless devices 110 may be avoided to protect private personalinformation. Instead, the signal decoder module 440 may decodeunencrypted control information such as handshaking messages (forexample, FIN, ACK, FIN ACK, and so forth). The signal decoder module 440may decode handshaking messages to identify devices using common mediumaccess signals like the MAC address of a device. Upon examining amodulation feature vector, the signal decoder module 440 may retrieveappropriate codecs and drivers from the signal database 450 for decodingthe signal. Outputs from the signal decoder module 440 may includeadditional features to be appended to the received modulation featurevectors. The additional features may include decoded contentrepresented, for example, as a binary sequence or other symbols.

The signal database 450 may provide a library of known signals to theraw signal analysis engines 240. According to certain embodiments, afeature vector of a known signal may be matched against or correlated toa received feature vector to classify modulation types and otherparameters associated with the received signal. The signal database 450may also provide codecs and drivers to the raw signal analysis engines240. The codecs and drivers may be used for decoding content of thereceived signal once its modulation type has been classified. It shouldbe appreciated that the signal database 450 may be provided as one ofthe analysis databases 380.

Outputs from the raw signal analysis engines 240 may comprise a set orstream of refined feature vectors. These feature vectors may have beenrefined from the received digital I and Q signal samples though one ormore iterations of processing by the various modules associated with theraw signal analysis engine 240. The outputs from the raw signal analysisengine 240 may be communicated onto the network 150 to be furtherprocessed through the other modules of the signal analysis system 130.The network 150 may comprise one or both of the raw digitalsignal-switching network 320 and the signal feature vector network 330.

Example Processes

According to methods and blocks described in the embodiments presentedherein, and, in alternative embodiments, certain blocks can be performedin a different order, in parallel with one another, omitted entirely,and/or combined between different example methods, and/or certainadditional blocks can be performed, without departing from the scope andspirit of the invention. Accordingly, such alternative embodiments areincluded in the invention described herein.

FIG. 5 is a block flow diagram depicting a method 500 forelectromagnetic signature analysis and threat detection in accordancewith one or more embodiments presented herein. In block 510, a pluralityof antennas 210 associated with sensors 120 may be provided. Theantennas 210 may be used to collect a broad range of radio frequencysignals from the electromagnetic environment for analysis. The antennas210 may be monopoles, dipoles, patch antennas, yagis, parabolic, horns,loops, reflector antennas, beam antennas, or any other type of structureconfigured to become electrically excited by radio frequencyelectromagnetic radiation of a desired frequency, polarization, orpropagation direction. The antennas 210 can be located in variouslocations around a room, around a building, or within different areas orfloors of a building

In block 520, an antenna signal-switching network 310 can supportswitching and routing radio frequency signals 215 received by theantennas 210 to various radio receivers. The radio frequency signals 215may be coupled from the antennas 210 using coaxial cable, otherconductive transmission, or optical fiber waveguides. The antennasignal-switching network 310 can support switching and routing the radiofrequency signals 215 from one particular antenna 210 between some orall of the receivers within the system. According to some embodiments,certain receivers may be directly coupled to certain antennas 210without being switchable.

In block 530, the radio frequency signals 215 received by the antennas210 may be coupled from the antenna signal-switching network 310 toradio receivers. The receivers may include both the software-definedradios 335 as well as the hardware-defined radios 340.

In block 540, a raw signal analysis engine 240 can process a digitalrepresentation of the raw collected radio frequency signal 215. The rawsignal analysis engine 240 may receive digital I and Q signal samples.The received samples may be processed and refined to a discrete set offeature vectors. A signal feature vector may be a set of valuesrepresenting attributes of the signal. Feature vectors may be passedfrom one stage of analysis or processing to another. At each step,attributes may be added or subtracted from the feature vector furtherrefining the attributes of the particular signal. Such refinement of thefeature vector may support identifying, classifying, or otherwiseinterpreting the content of the signal. Various modifiers or descriptorsindicating features or attributes of the signal may be appended to thefeature vectors at each processing step. Some examples of thesemodifiers or descriptors may include geolocation parameters, signalduration, signal bandwidth, signal angle, modulation type, and so forth.The raw signal analysis engine 240 may generate a raw signal analysisoutput 250. The raw signal analysis output 250 may be a condensedcollection of intelligible features and data as identified within thecollected radio frequency signal 215. According to one or moreembodiments, the signal data may be processed and refined into featurevectors that define various attributes of the signal.

It should be appreciated that a hardware-defined radio receiver 340 mayincorporate some or all of the features of the raw signal analysisengine 240. Outputs form the hardware-defined radio receiver 340 may bequite specific to the types of wireless communications handled by thehardware-defined radio receiver 340. For example, a hardware-definedradio receiver 340 intended to receive Wi-Fi may output data packetsinstead of feature vectors. The contents of the data packets may bereformatted into feature vectors along with any addition informationprovided by the hardware-defined radio receiver 340 such as signalstrength or wireless local area network configuration parameters such aschannel number, frequency, network identifiers, or so forth.

Additional information regarding operation of the raw signal analysisengine 240 is discussed with respect to FIG. 6.

In block 550, signal features identified by the raw signal analysisengine 240 may be transmitted into a signal feature vector network 330.The signal feature vector network 330 can switch and route signalfeature vectors between the raw signal analysis engines 240 and thevarious other modules associated with the signal analysis system 130.

In block 560, the signal analysis system 130 can aggregate and processthe various radio frequency signals 215 captured form theelectromagnetic environment by the sensors 120. Example modules of thesignal analysis system 130 may include space-time-frequency analysis350, geolocation 355, pair-wise link association 360, data throughputestimation 365, device classification 370, and attack classification375. Additional information regarding operation of the signal analysissystem 130 is discussed with respect to FIG. 7.

In block 570, analysis databases 380 may be managed. The analysisdatabases 380 may include, among various other examples, signaldatabases, sensor position databases, calibration databases, signalsignature databases, and attack databases. One or more of the signalprocessing and threat analysis stages of the signal analysis system 130,including the raw signal analysis engines 240, may leverage the analysisdatabases 380. The analysis databases 380 may contain various forms ofinformation useful in analyzing the radio frequency signals collected bythe sensors 120. Information within the analysis databases 380 may beupdated autonomously through automated learning, tuning, or adaptation.Portions of the information within the analysis databases 380 may beupdated from time to time from a central provider, from backups, or fromother installations. Managing the analysis databases 380 may includesharing locally updated information to other locations or to a centralprovider. Managing the analysis databases 380 may also include locallyupdating information received from other locations or from the centralprovider.

In block 580, a console 140 and various operator interfaces can supportconfiguring, controlling, or reviewing analysis results associated withthe signal analysis system 130. The console 140 can providevisualization features for use by security administrators to monitor theelectromagnetic environment for wireless security threats. Suchvisualization features may include displays about the area undersurveillance including device type, device locations, pair-wise wirelesscommunication links between devices, estimates of the data throughputbeing transmitted by devices, attack types being perpetrated, maliciousdevices, victim devices, and so forth. The console 140 may be a desktopcomputing machine or any other type of computing machine. The operatorinterfaces may support tablets, mobile devices, web or browser-basedapplications, alarm system interfaces, and the generation of variousreports to system administrators or security personnel.

FIG. 6 is a block flow diagram depicting a method 600 for raw signalanalysis in accordance with one or more embodiments presented herein. Inblock 610, a signal database 450 may be provided. The signal database450 may provide a library of known signals to the raw signal analysisengines 240. A feature vector of a known signal may be matched againstor correlated to a received feature vector to classify modulation typesand other parameters associated with the received signal. The signaldatabase 450 may also provide codecs and drivers to the raw signalanalysis engines 240. The codecs and drivers may be used for decodingcontent of the received signal once its modulation type has beenclassified.

In block 620, signal features may be identified though iteratedprocessing by the various modules associated with the raw signalanalysis engine 240. Digital signal samples received by the raw signalanalysis engine 240 may be processed and refined to a discrete set offeature vectors. A signal feature vector may be a set of valuesrepresenting attributes of the signal. Feature vectors may be passedfrom one stage of analysis or processing to another. At each step,attributes may be added or subtracted from the feature vector furtherrefining the attributes of the particular signal. Such refinement of thefeature vector may support identifying, classifying, or otherwiseinterpreting the content of the signal. During this hierarchical and/oriterative interpretation of the signal various modifiers or descriptorsindicating features or attributes of the signal may be appended to thefeature vectors at each processing step. Some examples of thesemodifiers or descriptors may include geolocation parameters, signalduration, signal bandwidth, signal angle, modulation type, and so forth.It should be understood that the feature vectors may be processed andre-processed by the various modules associated with the raw signalanalysis engine 240 any number of times before being transmitted to theother modules of the signal analysis system 130.

In block 630, the raw signal analysis engine 240 may receive digital Iand Q signal samples. The digitizers 230 may generate the samples fromthe signals collected at the antennas 210.

In block 640, the time-frequency analysis module 410 can generate a setof frequency-domain data vectors for each radio frequency signal 215.The spectrum intensity for each time-frequency bin associated with thefrequency-domain data vectors may be encoded as dimensions of featurevectors for each of the radio frequency signals 215. The time-frequencyanalysis module 410 can perform a fast Fourier transform (FFT) over afinite sample window. The FFT output may represent the spectral energycontent of the window. The output of the FFT may be a sequence offrequency-domain data vectors. The collection of these data vectors canbe plotted to show the time-frequency energy in the RF environment. Thisplot is commonly referred to as a spectrogram.

The time-frequency analysis module 410 can perform energy clustering andassociation. Energy clustering and association can perform a clusteringanalysis on each set of frequency-domain data vectors to determinediscrete contiguous blocks of signal that are likely to have beentransmitted from the same device. Spectrum feature extraction may beperformed on each cluster. Spectrum feature extraction can analyze theclusters to extract a set of signal features including, but not limitedto, duration, bandwidth, center frequency, duty cycle, and averagepower.

In block 650, the angle analysis module 420 can sweep through a range ofantenna phases. Various phase combinations of the antennas 210 may beused in order to discriminate the source of an emission by an anglerelative to the antennas 210. By sweeping through a range of values, theangle analysis module 420 can determine energies over aspace-time-frequency (STF) data cube. Angle interference suppression maybe performed on the STF data cube to filter out irrelevant RF signals.The angle analysis module 420 can then perform angle clustering andassociation on the filtered data cube. Angle clustering and associationcan refine the feature vector based on the angle information. Theresulting updated set of feature vectors may be referred to as anglefeature vectors. Each angle feature vector can include characteristicsabout each signal, such as duration, bandwidth, center frequency, dutycycle, average power, and angle.

In block 660, the modulation classification module 430 classifymodulation types by comparing the angle feature vectors to features of alibrary of known signals. The known signals may be retrieved from thesignal database 450. The modulation classification module 430 canperform classifications by matching an angle feature vector to a featurevector of a known signal. Outputs from the modulation classificationmodule 430 may be angle feature vectors that also include modulationtypes. These may be referred to as modulation feature vectors.

In block 670, the signal decoder module 440 can decode messaging layercontent from modulation feature vectors. Upon examining a modulationfeature vector, the signal decoder module 440 may retrieve appropriatecodecs and drivers from the signal database 450 for decoding the signal.The signal decoder module 440 may decode handshaking messages toidentify devices using common medium access signals like the MAC addressof a device. Outputs from the signal decoder module 440 may includeadditional features to be appended to the received modulation featurevectors. The additional features may include decoded contentrepresented, for example, as a binary sequence or other symbols.

In block 680, refined feature vectors may be generated. Outputs from theraw signal analysis engines 240 may comprise a set or stream of refinedfeature vectors. The outputs from the raw signal analysis engine 240 maybe communicated onto the network 150 to be further processed through theother modules of the signal analysis system 130.

FIG. 7 is a block flow diagram depicting a method 700 for feature vectoraggregation and analysis in accordance with one or more embodimentspresented herein. In block 705, analysis databases 380 may be provided.The analysis databases 380 may include, among various other examples,signal databases, sensor position databases, calibration databases,signal signature databases, and attack databases. One or more of thesignal processing and threat analysis stages of the signal analysissystem 130 may leverage the analysis databases 380. The analysisdatabases 380 may contain various forms of information useful inanalyzing the radio frequency signals collected by the sensors 120.

In block 710, the signal analysis system 130 can receive refined featurevectors. The refined feature vectors may be used in detecting,classifying, and mitigating wireless attacks against one or morewireless devices 110. Various digital signal processing stages may beapplied to the receive refined feature vectors. These digital signalprocessing stages may comprise modules of the signal analysis system130. Generally, a signal feature vector may be a set of valuesrepresenting attributes of a particular signal.

In block 715, the signal analysis system 130 can aggregate and furtherrefine feature vectors through the iteration of various processingmodules. Example modules of the signal analysis system 130 may includespace-time-frequency analysis 350, geolocation 355, pair-wise linkassociation 360, data throughput estimation 365, device classification370, and attack classification 375. As a feature vector is passed fromone processing module or stage to the next, attributes may be added orsubtracted from the feature vector, further refining the attributes ofthe particular signal to better identify and/or classify the contents ofthe signal. Feature vectors may be appended with various featureattributes relevant to the processing at each module or processingstage.

In block 720, the space-time-frequency analysis module 350 can processrefined feature vectors to match them to a common reference frame. Thespace-time-frequency analysis module 350 can also resolve redundantsignal detection when the same signal is detected at more than onesensor 120. The space-time-frequency analysis module 350 can performsignal clustering and association. Feature vectors from multiple sensors120 may be clustered into common groups. The space-time-frequencyanalysis module 350 can perform feature extraction. Feature extractioncan cull disparate refined feature vectors from multiple sensors 120into an aggregate feature vector that seeks to represent the informationabout wireless devices 110 in the environment with minimal, orsignificantly reduced, redundancy. Certain dimensions of aggregatedfeature vectors may provide identical values across multiple sensors120. These may include duration, bandwidth, center frequency, and dutycycle, among others. Certain other dimensions of aggregated featurevectors may be maintained as a list of potentially disparate values,with each value corresponding to a single sensor 120. For instance, thedimensions of the aggregate feature vectors representing a power and anangle of a signal may vary across sensors 120 due to the sensors beingin different locations.

In block 725, the geolocation module 355 analyzes received signals tolocate the position of wireless devices 110 within the electromagneticenvironment. Geolocating signals in an environment that is dense withother signals and contains complex propagation effects like multipathand Doppler shift can present several challenges. To aid in estimate theposition of each signal, propagation modeling may leverage a database ofsensor positions and various parameters associated with the propagationenvironment. The geolocation module 355 can carry out propagationmodeling using the calibration parameters along with information onsignal power and angle values, and a coordinate system of locations forthe sensors 120. These quantities may be used to calculate a forwardmodel of the expected power and angle values for sample points in space.These model values may be used to create an initial geolocation estimateusing multilateration techniques. The initial geolocation estimate maybe used to seed a model-matching filter. The model-matching filter canevaluate multiple aggregated feature vectors in series. For eachaggregate feature vector, the model-matching filter may initialize anensemble of hypothesized signal source positions around the initial seedposition. In an iterative process using the model values, a convergingestimate of the aggregate feature vector position may be generated foreach wireless device 110 being located. As part of each iteration,hypothesized positions that do not fit the model may be removed. After asufficient number of iterations, the position estimate for the aggregatefeature vector may converge to a single point. This approach may berepeated for all aggregate feature vectors.

In block 730, the pair-wise link association module 360 may determine alink pair of wireless devices 110. Generally a signal emanates from asource wireless device 110 and is intended for one or more destinationwireless devices 110. The emitting device and a receiving device mayconstitute a link pair. Information about link pairings may be useful ininferring the behavior and intent of wireless devices 110 within anetwork. Modulation association may be implemented within the pair-wiselink association module 360. Generally, wireless devices 110 within awireless network participate in pair-wise links between devices engagedin common or corresponding wireless features such as modulation,position, space-time-frequency occupancy, and so forth. Pair-wise linksmay also be determined by examining decoded message contents. Featurevectors successfully evaluated by the pair-wise link association module360 may be appended with a new set of feature vectors that contain thepairwise link information. It should be appreciated that thesetechniques used to associate pairs of communicating wireless devices 110may also apply to groups of three or more wireless devices 110 that arein communication with one another.

In block 735, the data throughput estimation module 365 can estimate anamount of data in each pairwise feature vector. Even when signal contentdata is not directly decoded, its spectral occupancy may serve as aproxy for the amount of data that is being passed through each linkwireless devices 110 associated with each pairwise feature vector. Thisestimation may occur on two levels. The first level, spectrogramanalysis, can use Shannon's capacity formula to bound the maximum amountof data transfer. The second level, modulation and link analysis, canleverage a signal signature database containing data throughput valuesfor various known signal modulation schemes. By pairing the modulationfeature values included in the pair-wise feature vector with the signalsignature database entries, modulation and link analysis can provide areasonably accurate estimate of the data throughput. An estimate of thedata throughput for each signal may be added to each correspondingpair-wise feature vector.

In block 740, the device classification module 370 can classify wirelessdevices 110 as being either benign or malicious (also referred to asunauthorized or rogue). Devices classification can function to identifyeach pairwise feature vector as either benign or malicious. The deviceclassification module 370 can perform signature matching, which attemptsto match the signal and link features of each data throughput featurevector to known examples of benign and malicious devices in the signalsignature database. The device classification module 370 can furtherperform anomaly analysis, which compares the features associated witheach data throughput feature vector into an aggregate metric. If theaggregate metric exceeds one or more established anomaly thresholds, theassociated wireless device 110 may be flagged as malicious orpotentially malicious. The device classification module 370 can alsoperform location analysis or geo-fencing, which evaluates thegeolocation features associated with each feature vector. If anunauthorized wireless device 110 is identified to be within in arestricted area, then the wireless device 110 may be flagged asmalicious or potentially malicious.

In block 745, the attack classification module 375 can determine thetype of attack being perpetrated by a malicious wireless device 110. Theattack classification module 375 can also determine if multiplemalicious wireless devices 110 are involved in the attack and whichvictim wireless devices 110 are being attacked. The attackclassification module 375 can support attack matching, which can use alibrary of attack templates to match malicious wireless device 110activities to known attacks such as spoofing, DoS, jamming, wormholes,and others discussed herein or known in the art.

In block 750, the signal analysis system 130 can cue resourcesassociated with the signal transmission and processing architecture.Processing of the various received signals can cue configurations of theantenna signal-switching network 310. The antenna signal-switchingnetwork 310 can support switching and routing radio frequency signals215 received by the antennas 210 to various radio receivers. The radioreceivers may include both the software-defined radios 335 as well asthe hardware-defined radios 340. One example of cueing configurations ofthe antenna signal-switching network 310 may involve rerouting areceived radio frequency signal 215 between a software-defined receiver335 and a hardware-defined receiver 340 based upon which receiver typebenefits overall system efficacy or efficient resource allocation.Similarly the antenna signal-switching network 310 may be cued to splitthe radio frequency signal 215 to both a software-defined receiver 335and a hardware-defined receiver 340 to allow the hardware-definedreceiver 340 to efficient extract and decode signal components specificto that receiver while the signal analysis system 130 focuses on othercomponents of that radio frequency signal 215 requiring specializedprocessing or multi-signal aggregation.

In block 755, the signal analysis system 130 can output feature vectorsthat have been refined through the iteration of various processingmodules. The signal feature vectors may be transported within the signalfeature vector network 330 to the console 140 or various otherapplications.

Example Systems

FIG. 8 depicts a computing machine 2000 and a module 2050 in accordancewith one or more embodiments presented herein. The computing machine2000 may correspond to any of the various computers, servers, mobiledevices, embedded systems, or computing systems presented herein. Themodule 2050 may comprise one or more hardware or software elementsconfigured to facilitate the computing machine 2000 in performing thevarious methods and processing functions presented herein. The computingmachine 2000 may include various internal or attached components such asa processor 2010, system bus 2020, system memory 2030, storage media2040, input/output interface 2060, and a network interface 2070 forcommunicating with a network 2080.

The computing machine 2000 may be implemented as a conventional computersystem, an embedded controller, a laptop, a server, a mobile device, asmartphone, a set-top box, a kiosk, a vehicular information system, onemore processors associated with a television, a customized machine, anyother hardware platform, or any combination or multiplicity thereof. Thecomputing machine 2000 may be a distributed system configured tofunction using multiple computing machines interconnected via a datanetwork or bus system.

The processor 2010 may be configured to execute code or instructions toperform the operations and functionality described herein, managerequest flow and address mappings, and to perform calculations andgenerate commands. The processor 2010 may be configured to monitor andcontrol the operation of the components in the computing machine 2000.The processor 2010 may be a general purpose processor, a processor core,a multiprocessor, a reconfigurable processor, a microcontroller, adigital signal processor (“DSP”), an application specific integratedcircuit (“ASIC”), a graphics processing unit (“GPU”), a fieldprogrammable gate array (“FPGA”), a programmable logic device (“PLD”), acontroller, a state machine, gated logic, discrete hardware components,any other processing unit, or any combination or multiplicity thereof.The processor 2010 may be a single processing unit, multiple processingunits, a single processing core, multiple processing cores, specialpurpose processing cores, co-processors, or any combination thereof.According to certain embodiments, the processor 2010 along with othercomponents of the computing machine 2000 may be a virtualized computingmachine executing within one or more other computing machines.

The system memory 2030 may include non-volatile memories such asread-only memory (“ROM”), programmable read-only memory (“PROM”),erasable programmable read-only memory (“EPROM”), flash memory, or anyother device capable of storing program instructions or data with orwithout applied power. The system memory 2030 also may include volatilememories, such as random access memory (“RAM”), static random accessmemory (“SRAM”), dynamic random access memory (“DRAM”), and synchronousdynamic random access memory (“SDRAM”). Other types of RAM also may beused to implement the system memory 2030. The system memory 2030 may beimplemented using a single memory module or multiple memory modules.While the system memory 2030 is depicted as being part of the computingmachine 2000, one skilled in the art will recognize that the systemmemory 2030 may be separate from the computing machine 2000 withoutdeparting from the scope of the subject technology. It should also beappreciated that the system memory 2030 may include, or operate inconjunction with, a non-volatile storage device such as the storagemedia 2040.

The storage media 2040 may include a hard disk, a floppy disk, a compactdisc read only memory (“CD-ROM”), a digital versatile disc (“DVD”), aBlu-ray disc, a magnetic tape, a flash memory, other non-volatile memorydevice, a solid sate drive (“SSD”), any magnetic storage device, anyoptical storage device, any electrical storage device, any semiconductorstorage device, any physical-based storage device, any other datastorage device, or any combination or multiplicity thereof. The storagemedia 2040 may store one or more operating systems, application programsand program modules such as module 2050, data, or any other information.The storage media 2040 may be part of, or connected to, the computingmachine 2000. The storage media 2040 may also be part of one or moreother computing machines that are in communication with the computingmachine 2000 such as servers, database servers, cloud storage, networkattached storage, and so forth.

The module 2050 may comprise one or more hardware or software elementsconfigured to facilitate the computing machine 2000 with performing thevarious methods and processing functions presented herein. The module2050 may include one or more sequences of instructions stored assoftware or firmware in association with the system memory 2030, thestorage media 2040, or both. The storage media 2040 may thereforerepresent examples of machine or computer readable media on whichinstructions or code may be stored for execution by the processor 2010.Machine or computer readable media may generally refer to any medium ormedia used to provide instructions to the processor 2010. Such machineor computer readable media associated with the module 2050 may comprisea computer software product. It should be appreciated that a computersoftware product comprising the module 2050 may also be associated withone or more processes or methods for delivering the module 2050 to thecomputing machine 2000 via the network 2080, any signal-bearing medium,or any other communication or delivery technology. The module 2050 mayalso comprise hardware circuits or information for configuring hardwarecircuits such as microcode or configuration information for an FPGA orother PLD.

The input/output (“I/O”) interface 2060 may be configured to couple toone or more external devices, to receive data from the one or moreexternal devices, and to send data to the one or more external devices.Such external devices along with the various internal devices may alsobe known as peripheral devices. The I/O interface 2060 may include bothelectrical and physical connections for operably coupling the variousperipheral devices to the computing machine 2000 or the processor 2010.The I/O interface 2060 may be configured to communicate data, addresses,and control signals between the peripheral devices, the computingmachine 2000, or the processor 2010. The I/O interface 2060 may beconfigured to implement any standard interface, such as small computersystem interface (“SCSI”), serial-attached SCSI (“SAS”), fiber channel,peripheral component interconnect (“PCI”), PCI express (PCIe), serialbus, parallel bus, advanced technology attachment (“ATA”), serial ATA(“SATA”), universal serial bus (“USB”), Thunderbolt, FireWire, variousvideo buses, and the like. The I/O interface 2060 may be configured toimplement only one interface or bus technology. Alternatively, the I/Ointerface 2060 may be configured to implement multiple interfaces or bustechnologies. The I/O interface 2060 may be configured as part of, allof, or to operate in conjunction with, the system bus 2020. The I/Ointerface 2060 may include one or more buffers for bufferingtransmissions between one or more external devices, internal devices,the computing machine 2000, or the processor 2010.

The I/O interface 2060 may couple the computing machine 2000 to variousinput devices including mice, touch-screens, scanners, biometricreaders, electronic digitizers, sensors, receivers, touchpads,trackballs, cameras, microphones, keyboards, any other pointing devices,or any combinations thereof. The I/O interface 2060 may couple thecomputing machine 2000 to various output devices including videodisplays, speakers, printers, projectors, tactile feedback devices,automation control, robotic components, actuators, motors, fans,solenoids, valves, pumps, transmitters, signal emitters, lights, and soforth.

The computing machine 2000 may operate in a networked environment usinglogical connections through the network interface 2070 to one or moreother systems or computing machines across the network 2080. The network2080 may include wide area networks (“WAN”), local area networks(“LAN”), intranets, the Internet, wireless access networks, wirednetworks, mobile networks, telephone networks, optical networks, orcombinations thereof. The network 2080 may be packet switched, circuitswitched, of any topology, and may use any communication protocol.Communication links within the network 2080 may involve various digitalor an analog communication media such as fiber optic cables, free-spaceoptics, waveguides, electrical conductors, wireless links, antennas,radio-frequency communications, and so forth.

The processor 2010 may be connected to the other elements of thecomputing machine 2000 or the various peripherals discussed hereinthrough the system bus 2020. It should be appreciated that the systembus 2020 may be within the processor 2010, outside the processor 2010,or both. According to some embodiments, any of the processor 2010, theother elements of the computing machine 2000, or the various peripheralsdiscussed herein may be integrated into a single device such as a systemon chip (“SOC”), system on package (“SOP”), or ASIC device.

In situations in which the systems discussed here collect personalinformation about users, or may make use of personal information, theusers may be provided with a opportunity to control whether programs orfeatures collect user information (e.g., information about a user'ssocial network, social actions or activities, profession, a user'spreferences, or a user's current location), or to control whether and/orhow to receive content from the content server that may be more relevantto the user. In addition, certain data may be treated in one or moreways before it is stored or used, so that personally identifiableinformation is removed. For example, a user's identity may be treated sothat no personally identifiable information can be determined for theuser, or a user's geographic location may be generalized where locationinformation is obtained (such as to a city, ZIP code, or state level),so that a particular location of a user cannot be determined. Thus, theuser may have control over how information is collected about the userand used by a content server.

One or more aspects of embodiments may comprise a computer program thatembodies the functions described and illustrated herein, wherein thecomputer program is implemented in a computer system that comprisesinstructions stored in a machine-readable medium and a processor thatexecutes the instructions. However, it should be apparent that therecould be many different ways of implementing embodiments in computerprogramming, and the invention should not be construed as limited to anyone set of computer program instructions. Further, a skilled programmerwould be able to write such a computer program to implement anembodiment of the disclosed invention based on the appended flow chartsand associated description in the application text. Therefore,disclosure of a particular set of program code instructions is notconsidered necessary for an adequate understanding of how to make anduse the invention. Further, those skilled in the art will appreciatethat one or more aspects of the invention described herein may beperformed by hardware, software, or a combination thereof, as may beembodied in one or more computing systems. Moreover, any reference to anact being performed by a computer should not be construed as beingperformed by a single computer as more than one computer may perform theact.

The example embodiments described herein can be used with computerhardware and software that perform the methods and processing functionsdescribed previously. The systems, methods, and procedures describedherein can be embodied in a programmable computer, computer-executablesoftware, or digital circuitry. The software can be stored oncomputer-readable media. For example, computer-readable media caninclude a floppy disk, RAM, ROM, hard disk, removable media, flashmemory, memory stick, optical media, magneto-optical media, CD-ROM, etc.Digital circuitry can include integrated circuits, gate arrays, buildingblock logic, field programmable gate arrays (“FPGA”), etc.

The example systems, methods, and acts described in the embodimentspresented previously are illustrative, and, in alternative embodiments,certain acts can be performed in a different order, in parallel with oneanother, omitted entirely, and/or combined between different exampleembodiments, and/or certain additional acts can be performed, withoutdeparting from the scope and spirit of embodiments of the invention.Accordingly, such alternative embodiments are included in the inventionsdescribed herein.

Although specific embodiments have been described above in detail, thedescription is merely for purposes of illustration. It should beappreciated, therefore, that many aspects described above are notintended as required or essential elements unless explicitly statedotherwise. Modifications of, and equivalent components or actscorresponding to, the disclosed aspects of the example embodiments, inaddition to those described above, can be made by a person of ordinaryskill in the art, having the benefit of the present disclosure, withoutdeparting from the spirit and scope of the invention defined in thefollowing claims, the scope of which is to be accorded the broadestinterpretation so as to encompass such modifications and equivalentstructures.

What is claimed is:
 1. A method for a sensor mesh and signaltransmission architecture for electromagnetic signature analysis andthreat detection, comprising: providing a plurality of sensor antennaswithin an electromagnetic environment; coupling radio frequency signalsfrom one or more of the sensor antennas into an antenna feed network;coupling radio frequency signals from the antenna feed network into oneor more radio receivers; performing raw signal analysis at one or moreof the radio receivers to identify signal features; transmitting thesignal features into a signal feature network in the form of signalfeature vectors; aggregating the signal feature vectors from the signalfeature network into one or more feature vector processors; processingthe signal feature vectors to refine the signal features within thesignal feature vectors; classifying wireless devices as malicious orbenign according to the signal features within the signal featurevectors; identifying wireless attacks according to the signal featureswithin the signal feature vectors; reconfiguring the antenna feednetwork according to the signal features within the signal featurevectors; and transmitting the refined signal feature vectors from theone or more feature vector processors to support operator interfaces. 2.The method of claim 1, wherein the antenna feed network comprises directconnections between the sensor antennas and the one or more radioreceivers.
 3. The method of claim 1, wherein the antenna feed networkcomprises radio frequency signal switches.
 4. The method of claim 1,wherein the antenna feed network comprises radio frequency signalsplitters.
 5. The method of claim 1, wherein the one or more radioreceivers comprises a software-defined radio.
 6. The method of claim 1,wherein the one or more radio receivers comprises a hardware-definedradio.
 7. The method of claim 1, wherein reconfiguring the antenna feednetwork comprises switching one of the radio frequency signals between asoftware-defined radio and a hardware-defined radio.
 8. The method ofclaim 1, wherein identifying signal features comprises decoding signalcontent.
 9. The method of claim 1, wherein one of the signal featurescomprises one of a duration, a bandwidth, a center frequency, a dutycycle, and an average power.
 10. The method of claim 1, wherein thesignal feature network comprises a packetized data network.
 11. Themethod of claim 1, further comprising retrieving information from one ormore analysis databases.
 12. The method of claim 1, wherein the operatorinterfaces comprise an administrative user interface application.
 13. Asensor mesh and signal transmission system for electromagnetic signatureanalysis and threat detection, comprising: a plurality of sensorantennas within an electromagnetic environment; an antenna feed networkconfigured to couple radio frequency signals from one or more of thesensor antennas to one or more radio receivers; a raw signal analysisengine associated with one of the radio receivers, the raw signalanalysis engine comprising one or more processing units, and one or moreprocessing modules configuring the one or more processing units toidentify signal features within the radio frequency signals and generatesignal feature vectors from the identified signal features; a signalfeature network configured to receive signal feature vectors transmittedfrom the raw signal analysis engine; and a signal aggregation andanalysis engine comprising one or more processing units, and one or moreprocessing modules configuring the one or more processing units to:aggregate the signal feature vectors; process the signal feature vectorsto refine the signal features within the signal feature vectors;identify wireless attacks according to the signal features within thesignal feature vectors; and reconfigure the antenna feed networkaccording to the signal features within the signal feature vectors. 14.The system of claim 13, wherein the signal aggregation and analysisengine is further configured to present information associated with therefined signal feature vectors to support an operator interface.
 15. Thesystem of claim 13, wherein the antenna feed network comprises one of adirect radio frequency interconnection, a radio frequency signal switch,and a radio frequency signal splitter.
 16. The system of claim 13,wherein the one or more radio receivers comprises one or asoftware-defined radio and a hardware-defined radio.
 17. The system ofclaim 13, wherein one of the signal features comprises one of aduration, a bandwidth, a center frequency, a duty cycle, and an averagepower.
 18. The system of claim 13, wherein the signal feature networkcomprises a packetized data network.
 19. The system of claim 13, furthercomprising one or more analysis databases.
 20. A sensor mesh and signaltransmission system for electromagnetic signature analysis and threatdetection, comprising: a plurality of sensor antennas within anelectromagnetic environment; a configurable antenna feed networkoperable to couple radio frequency signals from one or more of thesensor antennas to a software-defined radio receiver and from one ormore of the sensor antennas to a hardware-defined radio receiver; a rawsignal analysis engine associated with the software-defined radioreceiver, the raw signal analysis engine operable to receive digitalsamples of one of the radio frequency signals, identify signal featureswithin the digital samples, and generate signal feature vectors from theidentified signal features; a signal feature network configured toreceive the signal feature vectors generated by the raw signal analysisengine; and a signal aggregation and analysis engine operable to receivethe signal feature vectors from the signal feature network, aggregatethe signal feature vectors, process the signal feature vectors to refinethe signal features within the signal feature vectors, and identifywireless attacks according to the signal features within the signalfeature vectors; and one or more updatable analysis databases supportingoperations of the raw signal analysis engine and the signal aggregationand analysis engine.